Method for setting up a dialysis treatment in a dialysis machine

ABSTRACT

A method of setting up a dialysis treatment in a dialysis machine may include the steps of determining conditions of a dialysis treatment adapted to a specific patient, determining a first function (U(t)) of a first quantity (U) characterizing the dialysis treatment as a function of time (t), and determining a second function (C(t)) of a second quantity (C) characterizing the dialysis treatment. The first function (U(t)) satisfying the conditions of the dialysis treatment and corresponding to a curve having a defined shape. The second function (C(t)) is correlated with the first function (U(t)) by constants (M, N) determined experimentally and the second function (U(t)) corresponding to a curve having a shape of the same kind as the shape as the first curve.

The present invention relates to a method of setting up a dialysistreatment in a dialysis machine.

In general, dialysis machines are preset for carrying out dialysistreatments that are personalized for patients affected by renalinsufficiency. In other words, the dialysis machines have controldevices that make it possible to set up a dialysis treatment that isspecific to each patient on the basis of the medical instructions. As arule, a prescription for a patient affected by renal insufficiency andundergoing dialysis treatment comprises instructions relating to theweight loss that the patient should experience and to the amount ofsalts that the patient should receive in the form of ions during thedialysis treatment. Other data characterizing the dialysis treatment,such as the maximum weight loss in unit time tolerated by the patientand the duration of the dialysis treatment, can be obtained from thegeneral conditions of health and from the patient's physicalcharacteristics. The weight loss during a dialysis treatment is due toexpulsion of a proportion of the blood fluid.

For this purpose, a dialysis machine of known type comprises anextracorporeal blood circuit connected, in use, to the patient'scirculatory system, a dialysate circuit, and a filter through which theblood circuit conveys the blood fluid and the dialysate circuit conveysthe dialysate. The filter comprises a semipermeable membrane, whichseparates, in use, the dialysate from the blood fluid and permits anexchange of ions between the dialysate and the blood fluid and thetransfer of a proportion of the blood fluid through the membrane. Themachine further comprises an ultrafiltration pump for expelling adefined quantity of the patient's blood fluid from the dialysate circuitand through the membrane to achieve the aforesaid weight loss. Thereforethere is a biunique correspondence between the weight loss and thequantity of blood fluid expelled during the whole treatment and,similarly, between the weight loss in unit time, also called the rate ofweight loss, and the delivery of the ultrafiltration pump. However, thiscorrespondence is not valid in the case where the extracorporeal circuitis provided with an infusion bag that releases a flow of infusion fluidinto the blood circuit. In this case the weight loss in unit time willbe equal to the difference between the ultrafiltration flow rate and theinfusion flow rate.

The extent of ion exchange is a function of the concentration of saltsin the blood fluid and of the natraemia of the patient's blood fluid. Inother words, the quantity of salts transferred to the patient isdetermined by setting the concentration of ions of the dialysate anddepends on the ion concentration and on the conditions of the bloodfluid. The concentration of the dialysate is measured by determining theconductivity of the dialysate and is monitored during the dialysistreatment.

In less recent dialysis machines, the values of the weight loss in unittime and of the conductivity of the dialysate were kept constantthroughout the treatment and were kept relatively low owing to the factthat the patient was unable to tolerate high values, and in consequencethe dialysis treatments were extremely long.

The newer dialysis machines are provided with devices for setting up thetreatment, in which the values of the weight loss in unit time and ofthe concentration of salts in the dialysate are set in such a way thatthey vary as a function of time. This innovation in the field ofdialysis machines occurred as a result of research in which it was foundthat a high weight loss in unit time can be tolerated well by an averagepatient in the initial stage of treatment, whereas the critical stagewith regard to the weight loss in unit time is the final stage oftreatment, during which the patient has already lost a large part of theweight, in the form of blood fluid, and is able to tolerate a weightloss in unit time that is relatively low compared with the initialweight loss in unit time. Furthermore, research has also shown that thepatient's receptiveness to the administration of salts in the form ofions is greater in the final stage of treatment compared with thepatient's receptiveness in the initial stage of the treatment. Thus, thedata setting devices of the newest machines have adapted to theinnovations introduced by medical research and make it possible todefine both the function of the weight loss in unit time as a functionof time, and the function of the conductivity of the solution ofdialysate as a function of time.

Existing devices for setting up a dialysis treatment are based onvarious methods, some of which envisage the introduction of data onweight loss in unit time for a series of successive intervals of time ofthe treatment, so that a histogram is substantially defined. In the sameway, conductivity data are introduced for a series of time intervals soas to define a histogram. Determination of a histogram makes it possibleto define the parameters of the dialysis treatment with increasingprecision as the time intervals become shorter, so that the dialysistreatment can be tailored very accurately to the requirements of a givenpatient. However, these methods require the input of a value for eachbar of the histogram, and for this reason it takes a relatively longtime to set up the dialysis treatment.

Other less refined methods envisage the setting of only the initialvalues and final values of weight loss in unit time and of theconductivity of the dialysate solution and the duration of the dialysistreatment and constantly varying the weight loss in unit time and theconductivity between the initial value and the final value. Thesetting-up time is much shorter for these methods, but they do notpermit the setting up of optimum treatments for each patient.

The aim of the present invention is to provide a method of setting up adialysis treatment in a dialysis machine that does not have thedisadvantages of the prior art and, in particular, is accurate,increases the efficiency of the treatment and at the same time can beimplemented easily and quickly.

According to the present invention, a method is provided for setting upa dialysis treatment in a dialysis machine comprising the steps of:

determining the conditions (U₀, TWL, DT) of a dialysis treatment adaptedto a specific patient;

determining a first function (U(t)) of a first quantity (U)characterizing the dialysis treatment as a function of time (t), thefirst function (U(t)) satisfying the conditions (U₀, TWL, DT) of thedialysis treatment and corresponding to a curve having a defined shape;

determining a second function (C(t)) of a second quantity (C)characterizing the dialysis treatment, the second function (C(t)) beingcorrelated with the first function (U(t)) by constants (M, N) determinedexperimentally and the second function (U(t)) corresponding to a curvehaving a shape of the same kind as the shape as the first curve.

According to the present invention, once the function of the firstquantity has been set, the function of the second quantity is determinedautomatically, greatly reducing the time for setting up the dialysistreatment.

The present invention will now be described with reference to theaccompanying drawings, which illustrate one non-limitative embodimentthereof, in which:

FIG. 1 is a schematic view of a dialysis machine constructed accordingto the present invention;

FIGS. 2 to 7 are images displayed by a screen of the dialysis machine ofFIG. 1 during setting up of a dialysis treatment; and

FIG. 8 is a block diagram, showing the operating modes of the machine ofFIG. 1 in the stage of setting up of a dialysis treatment.

Referring to FIG. 1, reference 1 indicates the whole dialysis machinefor providing dialysis treatments for patients affected by renalinsufficiency. Machine 1 comprises apparatus 2 for preparing thedialysate, a dialysate circuit 3, a blood circuit 4, a filter 5 and adevice 6 for setting up the dialysis treatment. Dialysate circuit 3transports the dialysate along a path P1 through filter 5 and isconnected to apparatus 2, whereas the blood circuit 4, in use, isconnected to the circulatory system of a patient and conveys the bloodfluid along a path P2 through filter 5, in which the dialysate fluid andthe blood fluid are separated by a semipermeable membrane 7, acrosswhich the ions of the dialysate fluid are transferred to the bloodfluid, whereas the impurities contained in the blood fluid aretransferred to the dialysate. The degree of exchange depends on the ionconcentration of the dialysate and on the natraemia of the patient'sblood fluid. Along circuit 3, downstream from filter 5, there is abranch 8 for extraction of blood fluid and an ultrafiltration pump 9 forextracting a flow rate Q of blood fluid, which passes through filter 5.In practice, ultrafiltration pump 9 provides extraction of the part ofthe blood fluid that crosses the semipermeable membrane 7, and in thisway produces the patient's weight loss. Apparatus 2 provides supply ofthe concentration of salts in the form of ions to the dialysate, whereasa sensor 10 mounted on dialysate circuit 3 detects the electricalconductivity C of the dialysate, the electrical conductivity C beingcorrelated to the concentration of ions in the dialysate. Apparatus 2and ultrafiltration pump 9 are controlled by a control unit (not shown),which determines the variation of the concentration of salts and of thedelivery Q of the ultrafiltration pump 9.

Device 6 comprises a microprocessor 11, a keyboard 12 and a screen 13,which is interactive, of the “touch screen” type, and is subdivided intoa zone 14, in which there are touch keys 15 for navigating and forselecting the pages of an electronic notebook, a zone 16, with touchkeys 17 for controlling apparatus 2, and a zone 18 for displaying thevalues for setting up the dialysis treatment and the characteristiccurves of the dialysis treatment. Keyboard 12 includes hard keys 19,which include a key 19 for going into a SET MODE for setting up thedialysis treatment, a key 19 “+/−” for changing the values of the datafor setting up the dialysis treatment, and a key 19 for confirming thedata.

On selecting key 19 for access to the SET MODE, keys 15 appear,indicating PROFILING, “WL”, i.e. the option for setting the weight loss,and “C”, i.e. setting of conductivity. Two keys 17 permit selection ofthe modes “PC” (PROGRESSIVE CURVE) and “STEP” (histogram), which permitaccess respectively to the mode for selection of a curve of variation ofthe rate of weight loss as a function of time without discontinuities inthe first derivative and to a mode for setting a histogram, of a knowntype, of variation of the rate of weight loss as a function of time.Selection of key 17 “PC” supplies the image illustrated in FIG. 2 andincludes a Cartesian system 20, which shows time t on the ordinate and,on the abscissa, the hourly weight loss U expressed in kg/h, a box/touchkey 21 for input of the figure for total weight loss TWL, a box/touchkey 22 for input of the dialysis time DT, a box 23 for displaying thatoperation is in progressive curve mode, a box/touch key 24 for input ofthe initial value of weight loss in unit time, i.e. the maximum weightloss U₀ and a box/touch key 25 for input of a parameter P, whichcharacterizes the shape of the progressive curve. In use, the operatortouches box/key 21, which becomes activated, and by means of key 19“+/−” alters a predefined value of the total weight loss TWL untilbox/key 21 displays the value of the total weight loss TWL defined bythe therapy, and the operator confirms that value by means ofconfirmation key 19. In a similar manner, by using boxes/touch keys 22and 24 and keys 19, the operator inputs and confirms the values of DTand of U₀, respectively.

Once the operator has selected the “progressive curve” mode,microprocessor 11 makes reference to a group of predefined functionsU(t, P) characterizing the weight loss in unit time and parametrizedwith parameter P. The group of functions U(t,P) comprises a family ofstraight lines AA, a family of parabolas BB with their convexitypointing upwards, and a family of hyperbolas CC with their convexitypointing downwards. As an example, below are given the families offunctions U(t,P) that reflect the shapes of curves AA, BB and CCrespectively.

Functions U(t;P) with a straight-line relationship corresponding to thefamily of straight lines AA

 U=K·t+U ₀;

functions U(t,P) with a course with convexity upwards corresponding tothe family of parabolas BB

U=A·t ² +B·t+U ₀;

functions U(t,P) with a course with convexity downwards corresponding tothe family of hyperbolas CC $U = \frac{D}{E + {F \cdot t} + t^{2}}$

The progressive curve AA, BB, CC that is to be preselected correspondsto a function U(t) of the group stated above and depends on the valueassigned to the discriminating parameter P, which indicates thecurvature of the curve relating the value U₀ of the initial weight lossto a value of the final weight loss U_(f) for t=DT, and the value of theintermediate weight loss U_(i) for t=DT/2 according to the followingrelation: $U_{i} = {U_{f} + {P \cdot \frac{U_{0} - U_{f}}{100}}}$

in which P is expressed as a percentage and U_(f) is an unknown and isalways less than U₀, representing the maximum weight loss tolerated bythe patient. In other words, the intermediate value U_(i) of the weightloss is determined by parameter P.

Although the value of U_(f) is unknown, the value of P equal to fiftypercent indicates that the curve belongs to the family of straight linesAA, and microprocessor 11 calculates the value of K, imposing thefollowing condition: T  W  L = ∫₀^(D  T)(K ⋅ t + U₀) ⋅ t

This condition means that the total weight loss is equal to the areasubtended by a straight line belonging to the family of straight linesAA for determining coefficient K. Once the value of coefficient K isknown, microprocessor 11 calculates the values of the flow U as afunction of t and displays the straight line in the system of Cartesianaxes 20 as shown in FIG. 3.

Parameter P is variable over a range of variability between twenty andeighty percent and for values of P greater than fifty percent the curvebelongs to the family of parabolas BB, whereas for values of P less thanfifty percent the curve belongs to the family of hyperbolas CC. Thisrange of variability also requires that the value of U_(i) is alwaysbetween the value U₀ and the value U_(f).

Microprocessor 11 determines the coefficients A and B of the parabolafor each value of P between fifty percent and eighty percent, imposingthe following conditions:

U _(i) =A·(^(DT)/₂)² +B·DT/2+U ₀ for t=DT/2;

U _(f) =A·DT ² +B·DT+U ₀ for t=DT;

${U_{i} = {{U_{f} + {{P \cdot \frac{U_{0} - U_{f}}{100}}\quad {for}\quad 50}} < P < 80}};$T  W  L = ∫₀^(D  T)(A ⋅ t² + B ⋅ t + C) ⋅ t.

In the four-equation system, the values DT, TWL, U₀ and P are known,whereas the unknowns are U_(f), U_(i), A and B, which vary ascoefficient P varies.

Substantially similarly, the coefficients D, E, and F of the hyperbolaare determined by microprocessor 11 for each value of parameter Pbetween fifty percent and 20 percent with the following system ofequations:

U ₀ =D/E for t=0;

${U_{i} = {{\frac{D}{E + {F \cdot \frac{D\quad T}{2}} + \left( \frac{D\quad T}{2} \right)^{2}}\quad f\quad o\quad r\quad t} = \frac{D\quad T}{2}}};$${U_{f} = {{\frac{D}{E + {{F \cdot D}\quad T} + {D\quad T^{2}}}\quad f\quad o\quad r\quad t} = {D\quad T}}};$${U_{i} = {{U_{f} + {{P \cdot \frac{U_{0} - U_{f}}{100}}\quad f\quad o\quad r\quad 20}} < P < 50}};$${T\quad W\quad L} = {\int_{0}^{D\quad T}{\left( \frac{D}{E + {F \cdot t} + t^{2}} \right) \cdot {{t}.}}}$

In the five-equation system, the values DT, TWL, U₀ and P are known,whereas the unknowns are U_(f), U_(i), D, E and F, which vary withvariation of coefficient P.

In practice, once we have predefined the group of functions U(t;,P):${U = {{K \cdot t} + U_{0}}};{U = {{A \cdot t^{2}} + {B \cdot t} + U_{0}}};{U = \frac{D}{E + {F \cdot t} + t^{2}}}$

the imposing of boundary conditions TWL, U₀, and DT selects a subset ofthe group of functions U(t,P) whereas assignment of a defined value toparameter P isolates a single function U(t) from the subset, so that thesystems of equations become defined.

From the operational standpoint, once the values TWL, U₀ and DT havebeen assigned, the operator varies parameter P by touching the box/touchkey 25 and key 19 “+/−” and microprocessor 11 displays, on screen 13,the curve corresponding to the value assigned to parameter P anddisplayed in the respective box/key 25. Referring to FIG. 3, each curvedisplayed satisfies the values TWL, U₀, and DT established on the basisof the doctor's prescription, therefore from the quantitative standpointthe therapeutic values are satisfied. The operator can select thequalitative course of administration for each patient by visuallyselecting the curve that belongs to one of the families AA, BB, CC andis best suited to the characteristics of the given patient by varyingparameter P. Together with the system of Cartesian axes 20, a bar 26 isdisplayed, which is parallel to the ordinate, is positioned tocorrespond to the value DT/2, and intercepts the curve at point U_(i).

The course of the concentration C(t) of the dialysate as a function oftime is determined similarly. In this case, screen 13 supplies the imageof FIG. 4 which shows a cartesian system 27, which has an abscissashowing the scale for time t and an ordinate showing the scale forconductivity C expressed in mS/cm (millisiemens per centimeter), abox/touch key 28 for input of the initial and maximum conductivity C₀, abox/touch key 29 for input of the final conductivity C_(f), a box 30 fordisplaying the progressive curve mode, a box/touch key 31 for inputtingthe dialysis time DT and a box/touch key 32 for inputting parameter P.

With variation of parameter P, the progressive curve belongs to a familyof straight lines A1 for P equal to fifty percent, to a family ofparabolas B1 with convexity upwards for P for a value greater than fiftypercent, and to a family of hyperbolas C1 for a value of P less thanfifty percent.

Functions C(t) with a straight-line course corresponding to the familyof straight lines A1 for P equal to 50% are as follows:

C=K·t+C _(0;)

functions C(t) corresponding to the family of curves B1 are as follows:

C=A·t ² +B·t+C _(0;)

functions C(t) corresponding to the family of curves C1 are as follows:$C = {\frac{D}{E + {F \cdot t} + t^{2}}.}$

In this case there is a change in boundary conditions for determiningthe unknowns. With regard to the straight line it is stipulated that

C _(f) =KDT+C ₀ for t=DT;

in which the unknown is K, whereas C_(f), DT and C₀ are known.

For a value of P greater than fifty percent the curve belongs to thefamily of parabolas B1 and the following conditions are imposed:

C _(i) =A·(^(DT)/₂)² +B· ^(DT)/₂ +C ₀ for t=DT/2;

C _(f) =A·DT ² +B·DT+C ₀ for t=DT;

$C_{i} = {{U_{f} + {{P \cdot \frac{C_{0} - C_{f}}{100}}\quad f\quad o\quad r\quad 50}} < P < 80}$

In the three-equation system, A, B and C_(i) are unknowns and C₀, C_(f),DT and P are known and are entered by the operator.

For a value of P less than fifty percent the curve belongs to the familyC1 and the following conditions are imposed:

C ₀=^(D)/_(E) for t=0;

${C_{i} = {{\frac{D}{E + {F \cdot \frac{D\quad T}{2}} + \left( \frac{D\quad T}{2} \right)^{2}}\quad f\quad o\quad r\quad t} = \frac{D\quad T}{2}}};$${C_{f} = {{\frac{D}{E + {{F \cdot D}\quad T} + {D\quad T^{2}}}\quad f\quad o\quad r\quad t} = {D\quad T}}};$$C_{i} = {{C_{f} + {{P \cdot \frac{C_{0} - C_{f}}{100}}\quad f\quad o\quad r\quad 20}} < P < 50.}$

In the four-equation system, D, F, F and C_(i) are unknowns and C₀,C_(f), DT and P are known and are entered by the operator.

In a similar manner to the preceding case, for each parameter P an imageis supplied for the respective curve belonging to one of the familiesA1, B1 and C1 as illustrated in FIG. 5. All the curves that aredisplayed satisfy the conditions imposed by the operator, who can selectthe curve visually that is the most suitable for the patient undergoingthe dialysis treatment.

According to the variant in FIGS. 6 and 7, the submenu activated byselecting “SET MODE” offers the options “WL” and “CS”, which replacesthe “C” mode and provides for stipulating the total quantity of saltsthat must be transferred to the patient. Selection of option “CS”determines display of the image of FIG. 6, which shows a Cartesiansystem 34 that has an abscissa for plotting the time t, and an ordinatefor plotting the electrical conductivity C, a box/touch key 35 for inputof data relating to the quantity of salts CS to be transferred to thepatient, a box/touch key 36 for entering the dialysis time DT, a box 37for displaying the progressive curve mode, a box/touch key 38 forentering the initial and maximum conductivity C₀, box/touch key 39 forentering discriminating parameter P and a box/touch key 40 for input ofa function FF.

Function FF is an absorption function based on algorithms of a knowntype that make reference to the characteristics of filter 5 and to theequivalent conductivity that is determined on the basis of the generalcharacteristics of a given patient, for whom the dialysis treatment isrequired.

With variation of parameter P, the curves are for example represented bythe curves A1, B1 and C1.

In the case when P is equal to fifty percent, the curve belongs tofamily A1 and the conditions imposed are as follows:${C_{i} = {C_{f} + \frac{C_{0} - C_{f}}{2}}};$${C_{i} = {\frac{{K \cdot D}\quad T}{2} + C_{0}}};$C  S = ∫₀^(D  T)F  F(t) ⋅ (K ⋅ t + C₀)t.

In the case when P is between fifty and eighty percent, the curvebelongs to the family of curve B1 and the conditions imposed are asfollows:

 C _(i) =A·(^(DT)/₂)² +B· ^(DT)/₂ +C ₀ for t=DT/2;

C _(f) =A·DT ² +B·DT+C ₀ for t=DT;

$C_{i} = {{U_{f} + {{P \cdot \frac{C_{0} - C_{f}}{100}}\quad f\quad o\quad r\quad 50}} \vartriangleleft P \vartriangleleft 80}$C  S = ∫₀^(D  T)F  F(t) ⋅ (A ⋅ t² + B ⋅ t + C) ⋅ t

In the four-equation system, the unknowns are C_(f), C_(i), A and B,whereas P, DT, CS, C₀ and the function FF(t) are known.

In the case when P is between twenty percent and fifty percent, thecurve belongs to the family of curves C1 and the boundary conditions areas follows:

C ₀=^(D)/_(E) for t=0;

${C_{i} = {{\frac{D}{E + {F \cdot \frac{D\quad T}{2}} + \left( \frac{D\quad T}{2} \right)^{2}}\quad f\quad o\quad r\quad t} = \frac{D\quad T}{2}}};$${C_{f} = {{\frac{D}{E + {{F \cdot D}\quad T} + {D\quad T^{2}}}\quad f\quad o\quad r\quad t} = {D\quad T}}};$${C_{i} = {{C_{f} + {{P \cdot \frac{C_{0} - C_{f}}{100}}\quad f\quad o\quad r\quad 20}} < P < 50}};$${C\quad S} = {\int_{0}^{D\quad T}{F\quad {{F(t)} \cdot \left( \frac{D}{E + {F \cdot t} + t^{2}} \right) \cdot {{t}.}}}}$

In the five-equation system the unknowns are C_(f). C_(i), D, E and F,whereas CS, P, C₀, DT and FF(t) are known.

Once the coefficients of the curve corresponding to the assigned valueof P are known, microprocessor 11 displays the curve in FIG. 7, and theoperator visually monitors the course of the curve with variation oftime. On the basis of visual monitoring and the patient'scharacteristics, the operator alters the value of P if he considers thatthe course must be corrected, or confirms with hard key 19 of keyboard12 if the course of the curve is appropriate to the characteristics of agiven patient.

Also when determining the conductivity function C(t), the curve isselected from among a group of functions C(t,P) parametrized withparameter P and a subset of functions C(t,P) is selected, imposing theboundary conditions DT, C₀ and C_(f) or CS, FF(t), DT and C₀ and,finally, function C(t) is preselected by selecting a defined value ofparameter P.

According to another variant, having determined the function U(t) andthe respective curve, i.e. the variation of weight loss as a function oftime t, the screen shows a touch key 17, which offers the option“MIRRORING” for determining function C(t) and the respective curve, i.e.the variation of the conductivity C as a function of time using only thedata that were entered in connection with determination of curve U(t)and two constants M and N, which have previously been entered in thememory of microprocessor 11.

The option “MIRRORING” imposes the condition that the difference betweeninitial flow U₀ and final flow U_(f) expressed in liters/hour is equalto the difference between the initial conductivity C₀ and the finalconductivity C_(f) expressed in mS/cm (millisiemens per centimeter) fora known proportionality factor N. This relation is expressed by equationNN:

[U _(O) −U _(F)]_(l/h) =N·[C ₀ −C _(ƒ)]_(mS/cm).

The option “MIRRORING” also stipulates that the initial flow U expressedin liters/hour is equal to the initial conductivity C expressed in mS/cmfor a constant M. This relation is expressed by equation MM:

[U _(O)]_(l/h) =M·[C ₀]_(mS/cm).

The option “MIRRORING” further envisages that curve C(t) should have thesame qualitative course as curve U(t), i.e. that parameter P should bethe same for both curves. Obviously the treatment time DT is the same.Therefore, the values of C₀ and C_(f) can be obtained from equations NNand MM, whereas DT and P are known, and accordingly it is possible toimpose the conditions for determining the coefficients of the curve inthe manner described previously.

In practice, three different means have been described for determiningthe course of the function C(t) and of the respective curve. Thesedifferent means can coexist in the device 6 for setting up the dialysistreatment.

Referring to FIG. 8, the operations of setting up the dialysis treatmentare shown schematically as a block diagram. Block 100 indicatesselection of key 19 “SET MODE”, which gives access to the options “WL”(block 110), option “C” (CONDUCTIVITY) and CS (CONDUCTIVITY/SALT)grouped in block 220. Selection of option WL gives access to selectionbetween the option “PROGRESSIVE CURVE” (block 120) and the option “STEPCURVE” (block 115). Selection of the option “PROGRESSIVE CURVE” givesaccess to block 130 for input of data U₀, DT and TWL and to block 140for input/change of P. Assignment of a value of P determines thatverification (block 150) of whether P is greater than, equal to or lessthan 50 is executed. For P equal to 50, microprocessor 11 calculatescoefficient K of one of the families of straight lines AA (block 160).For P>50, microprocessor 11 calculates the coefficients A and B of aparabola of family BB (block 170) and for P less than 50, microprocessor11 calculates the coefficients D, E and F of a hyperbola of family CC(block 180). Once the coefficients of the function corresponding to agiven value of P and to a given curve have been calculated,microprocessor 11 displays the curve determined by the value assigned toP on screen 13 with reference to Cartesian system 20. Once the curve isdisplayed, the operator decides (block 200) whether to modify the curveby entering a new value of P (block 140) so that microprocessor 11repeats the operations shown schematically in the blocks from 150 to 190for displaying the curve corresponding to the new value assigned toparameter P or for confirming the curve (block 210). Changing ofparameter P is repeated until the operator considers that the curve issuitable for setting up the dialysis treatment. Confirmation (block 210)is effected by means of a confirmation key (HARD KEY) 19. Once the curvecorresponding to function U(t) has been confirmed, the operator hasthree options for defining the course of the conductivity function C(t)with variation of time t. Options C and CS have already been describedand have been combined in block 220 as they only differ from one anotherin regard to the data that are entered by the operator. The option“MIRRORING” (block 330) prevents the input of the data as obtained fromthe data supplied for defining the curve of U(t) and from the constantsM and N obtained experimentally. Selection of the option C/CS offers theoptions “PROGRESSIVE CURVE” and “STEP CURVE”. Selection of “PROGRESSIVECURVE” determines presentation of the input of data (block 240) which,in the case of option “C”, are substantially C₀ and C_(f), since DT isknown and, in the case of option “CS”, are substantially CS, C₀ andFF(t), since DT is known. Parameter P is entered (block 250) andcompared with the discriminating value 50 (block 260) for determiningthe coefficients of the functions corresponding to the families ofcurves A1, B1 and C1. The curve of function C(t) corresponding to thevalue of P is displayed on screen 13 (block 300) and the operator hasthe option of deciding (block 310) whether to change the value of P(block 250) and whether to confirm the curve displayed (block 320) bymeans of a hard key 19.

Selection of the option “MIRRORING” determines calculation of C₀ andC_(f) (block 340), after which calculation of the coefficients of afunction C(t) corresponding to a curve belonging to the families A1, B1and C1, display of the curve and confirmation (blocks from 260 to 320)are effected in the same way as for option C. If the curve displayed bymeans of the MIRRORING operations does not satisfy the operator, thecurve is altered by varying the value of P (block 250) and themicroprocessor repeats the operations between blocks 260 and 310.

According to another variant, if the operator considers that some valuesof the curve do not satisfy the therapeutic requirements he also changesthe values of the initial conductivity C₀, final conductivity C_(f) andquantity of salts to be transferred to the patient CS.

In other words, the “MIRRORING” operation is able to supply a curve thatis acceptable in itself, or a base curve that is close to the acceptablecurve and can be altered for adapting the curve to the therapeuticrequirements.

In the example described, the function U(t) of weight loss in unit timecorresponds in fact to the delivery Q(t) of the ultrafiltration pump 9and setting the weight loss means setting the operation of theultrafiltration pump during the dialysis treatment. According to anothervariant that is not shown, the extracorporeal circuit is provided withan infusion bag that releases a flow I of infusion fluid into theextracorporeal circuit. In this case the ultrafiltration flow Q is equalto the sum of the weight loss U in unit time and the infusion flow.

What is claimed is:
 1. Method of setting up a dialysis treatment in adialysis machine (1) comprising the steps of: determining conditions ofa dialysis treatment adapted to a specific patient; determining a firstfunction (U(t)) of a first quantity (U) characterizing the dialysistreatment as a function of time (t), the first function (U(t))satisfying said conditions of the dialysis treatment and correspondingto a curve having a defined shape; and determining a second function(C(t)) of a second quantity (C) characterizing the dialysis treatment,the second function (C(t)) being correlated with the first function(U(t)) by constants (M, N) determined experimentally and the secondfunction (C(t)) corresponding to a curve having a shape of the same kindas the shape of the first curve.
 2. Method according to claim 1, whereinthe dialysis machine (1) comprises: an extracorporeal blood circuit (4)for the circulation of blood in a first compartment of a dialyzer (5)having first and second compartments separated by a semipermeablemembrane (7), a dialysate circuit (3) for conveying a dialysate in thesecond compartment of the dialyzer (5), the dialysate having a definedconcentration of salts which is correlated to the electricalconductivity (C) of the dialysate, an apparatus (2) for varying theconcentration of salts in the dialysate during the dialysis treatment,and an ultrafiltration pump (9) with variable delivery (Q) forextracting plasma water from the blood circulated in the extracorporealblood circuit (4) and causing a weight loss (TWL) during the dialysistreatment, wherein the first quantity is the weight loss (U) in unittime which is correlated to the delivery (Q) of the ultrafiltration pump(9), and the second quantity is the conductivity (C) of the dialysate.3. Method according to claim 2, wherein the constants (M, N) comprise afirst constant (M), which relates a first value (U₀) of the weight loss(U) in unit time at the initial moment of the dialysis treatment to avalue (C₀) of the conductivity (C) of the dialysate at the initialmoment of the dialysis treatment, and a second constant (N) that relatesthe difference between the first value (U₀) and a third value (U_(f)) ofthe weight loss (U) in unit time at the final moment of the dialysistreatment to the difference between the second value (C₀) and a fourthvalue (C_(f)) of the conductivity (C) of the dialysate at the finalmoment of the dialysis treatment, the first and third values (U₀, U_(f))being known from the first function.
 4. Method according to claim 3,wherein the dialysis machine (1) comprises a device (6) for setting upthe dialysis treatment comprising a microprocessor (11), data input (12,13) and a screen (13), the method comprising the steps of: supplying afirst group of functions (U(t,P)) characterizing the weight loss (U) inunit time as a function of time (t) and a variable parameter (P) that iscorrelated with intermediate values (U_(i)) of each function (U(t;P)) ofthe first group; selecting a subset of the group of functions (U(t;P))imposing the conditions of the dialysis treatment adapted to a specificpatient; assigning values to the parameter (P) and displaying the curvescorresponding to the functions (U(t,P)) of the subset and to therespective values assigned to the parameter (P); and selecting one ofthe functions ((U(t,P)) of the subset on the basis of the images of thecurves.
 5. Method according to claim 4, wherein the conditions of thedialysis treatment comprise the total weight loss (TWL), the dialysistime (DT) and the first value relative to the weight loss (U₀) in unittime at the initial moment of the dialysis treatment.
 6. Methodaccording to claim 4, wherein the parameter (P) is characteristic of thecurvature of each first curve correlated with a respective firstfunction ((U(t)) of the subset, and the determination of the secondfunction (C(t)) comprises the steps of: supplying a second group offunctions C(t,P)), determining a subset of second functions C(t,P)) thatsatisfy the correlation with the first function (U(t)) by means of thefirst and second constants (M, N) and are parameterised with theparameter (P), and supplying a second function (C(t)) having the samevalue of parameter (P) as the first function (U(t)).
 7. Method accordingto claim 6, wherein each first curve is displayed relative to aCartesian system (20) on the screen (13), the parameter (P)discriminating whether the curve is a straight line, whether the curvehas its curvature oriented in one direction or whether the curve has itscurvature oriented in the opposite direction, and determining the degreeof curvature.
 8. Method according to claim 6, comprising the step ofsupplying the image on the screen (13) of the second curve correlatedwith the said second function (C(t)).
 9. Method according to claim 8,comprising the step of varying the value assigned to parameter (P) foraltering the shape of the second curve and the respective secondfunction C(t)).
 10. Method according to claim 8 or claim 9, comprisingthe step of altering the second curve by varying the value of theinitial conductivity (C₀).
 11. Method according to claim 8 or claim 9,comprising the step of altering the second curve by varying the value ofthe final conductivity (C_(f)).
 12. Device for setting up a dialysistreatment comprising a microprocessor, a data input and a screen, thedevice being able to perform a method as claimed in claim
 1. 13. Amachine comprising: an apparatus for preparing a dialysate; a dialysatecircuit; a blood circuit; and a filter connected to the apparatus andthe blood circuit, and further comprising a device for setting up adialysis treatment according to claim
 12. 14. Method according to claim10, comprising the step of altering the second curve by varying thevalue of the final conductivity (C_(f)).